How gold-platinum cubes are proving the future of gravitational wave detection
In short: To detect ripples in space-time, scientists must achieve the most precise free-fall ever recorded. LISA Pathfinder achieved this by suspending gold-platinum cubes in a vacuum, testing whether we can observe Einstein's predicted gravitational waves from the silence of space rather than from Earth.
Launched in December 2015, the LISA Pathfinder mission traveled 1.5 million km from Earth toward the Sun to begin its scientific work on 1 March. The mission's primary objective was to test the feasibility of observing gravitational waves—fluctuations in the fabric of space-time predicted by Albert Einstein a century ago—from a space-based platform. To do this, the spacecraft utilized two identical gold-platinum cubes held in a state of near-perfect free-fall. This mission reached its operational orbit located 1.5 million km from Earth. It successfully commenced its scientific mission on 1 March.
The mission's performance was analyzed over approximately 500 days of science operations. Researchers focused on the differential acceleration of these test masses to understand the noise levels that might interfere with future missions. They discovered that at higher frequencies (above 1 mHz), the dominant noise was Brownian noise, which appeared to decay as gas pressure decreased due to the outgassing of a single gaseous species.
However, the environment was not perfectly quiet. Between 36 μHz and 1 mHz, the acceleration noise showed a 1/f tail that fluctuated by about 20% over several days. At the lowest frequency of 18 μHz, the noise deviated from this 1/f behavior due to temperature fluctuations that modulated a pressure gradient caused by asymmetrical outgassing. Although these results are intricate, they offer vital information for the upcoming LISA mission, given that known sources represent about 40% of the 1/f tail's noise power. Scientists identified that specific noise sources account for nearly 40% of the power in the 1/f tail. Researchers also investigated the remaining unexplained fraction to determine control measures for the future LISA mission.
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Sources
- Summary by Intellect · source: LISA Pathfinder results
- Also: In-depth Analysis of LISA Pathfinder Performance Results: Time Evolution, Noise Projection, Physical Models, and Implications for LISA - NASA Technical Reports Server (NTRS)
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